BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to an image forming apparatus and a fixing apparatus
provided thereto and, in more particularly, to an apparatus for forming an unfixed
toner image on a surface of a recording material by appropriate image forming processing
means such as electrophotography, electrostatic recording and magnetic recording including
a copier, a printer and a facsimile, using a toner made from a heat melting resin
and so on by a direct or indirect method, and heating and fixing it on the surface
of the recording material as a permanently fixed image by heating and fixing means.
Related Background Art
[0002] In an image forming apparatus, a fixing apparatus of a heat-roller method is widely
used as a heating means for fixing an unfixed toner image formed on a recording material
by an appropriate image forming processing means. The fixing apparatus of the heat-roller
method keeps in contact a fixing roller as a heating member incorporating a heat generating
means such as a halogen heater and a pressure roller as a pressure member so as to
fix the unfixed toner image by applying heat and pressure while transporting the recording
material.
[0003] In recent years, a fixing apparatus of a film heating method is rendered commercially
practical from viewpoints of a quick start and energy conservation. The fixing apparatus
of the film heating method is the one wherein a fixing nip is formed by having a heat-resistant
thin film sandwiched between a ceramic heater as heat generating means and a pressure
roller as a pressure member. It fixes the unfixed toner image by rotating the film
and the pressure roller together to apply the heat and pressure while transporting
the recording material. The film is heated by the ceramic heater at the fixing nip.
The ceramic heater has its temperature sensed by a temperature sensing element provided
on the back thereof, and energization to the ceramic heater is controlled and temperature
control thereof is performed based on the results of the sensing.
[0004] As for the above fixing apparatus of the film heating method, heat capacity of the
film as a heating member is very small compared to the heat-roller method, and so
it is possible to efficiently use thermal energy from the heat generating means in
a fixing process. For this reason, a temperature rising speed of the fixing apparatus
is fast so that waiting time between power-up of the apparatus and a printable state
thereof can be rendered shorter (quick start). In addition, there is no need to preheat
the heating member during standby for printing so that power consumption of the image
forming apparatus can be held low (energy conservation).
[0005] There is a proposal, as a fixing apparatus of a further high-efficiency film heating
method, of the fixing apparatus of the electromagnetic induction heating method for
causing a conductive film itself to generate heat. Japanese Utility Model Application
Laid-Open No. 51-109739 discloses, as the fixing apparatus of the electromagnetic
induction heating method, the fixing apparatus for having an eddy current induced
to a metallic film by an alternating magnetic field to cause the metallic film to
generate heat with Joule heat. As it is possible to cause the film itself to generate
heat by the electromagnetic induction heating method, the thermal energy from the
heat generating means can be used further efficiently in the fixing process.
[0006] Hereafter, the temperature control of the fixing apparatus on a start of printing
will be described.
[0007] FIG. 23 is a schematic view showing a fixing film temperature, a target temperature
setting and timing of recording material reaching the fixing apparatus when starting
the printing in the fixing apparatus of the past fixing apparatus (the fixing apparatus
of the film heating method using the ceramic heater or the fixing apparatus of the
electromagnetic induction heating method/film heating method).
[0008] Although the temperature control is off and no preheating is performed during standby
for printing, preheating may also be performed. The image forming apparatus starts
an image forming operation after receiving a print signal. The image forming apparatus
starts power supply to the fixing apparatus at the same time, and increases the temperature
of the fixing apparatus to a fixing temperature T
f. And the fixing apparatus keeps the fixing temperature T
f and prepares for fixing of the unfixed toner image on the recording material. The
above steps will be collectively called a starting step of the fixing apparatus.
[0009] In the starting step of the fixing apparatus, the recording material are not put
through paper so that most of the heat from the heat generating means is used to increase
the temperature of the pressure roller via a film. In particular, in the case where
the fixing apparatus is already warmed up, time t
wu for rising to the target temperature is short and time tp - t
wu for keeping the fixing temperature T
f is long, so that the temperature of the pressure roller further rises. For this reason,
the temperature of the pressure roller is apt to rise excessively in the case where
the starting step is repeated as with intermittent printing.
[0010] In the case of fixing the recording material requiring a lot of heat capacity for
the fixing such as a cardboard or an OHT film in general, processing speed is reduced.
In the stating step in such a case, time tp from the start of the image forming operation
until the recording material reaches the fixing apparatus becomes longer, and so the
time t
p - t
wu for keeping the recording material at the fixing temperature T
f without putting it through paper becomes longer. For this reason, the temperature
of the pressure roller is apt to rise excessively as with the intermittent printing.
[0011] As described above, there is a problem that, if the printing is performed in a state
in which the temperature of the pressure roller has excessively risen, slipping of
the recording material is apt to occur. It is because moisture in the recording material
evaporates on the heating and fixing and frictional force between the pressure roller
and the recording material is reduced. In particular, the higher the temperature of
the pressure roller is, the more the amount of evaporated moisture becomes, and so
the slipping of the recording material is more likely to occur. Furthermore, the slipping
of the recording material occurs more conspicuously in the case of the fixing apparatus
of the film heating method wherein a driving force is applied to the pressure roller
and the film is rotated by being slaved to the pressure roller.
[0012] There was a problem that, if the slipping of the recording material occurs, the recording
material does not move along a carriage guide member or winds itself around the film,
resulting in occurrence of a jam. Furthermore, there was a problem that, as it is
not possible to stably apply the heat and pressure to the unfixed toner image, quality
of a fixed image is lowered.
SUMMARY OF THE INVENTION
[0013] An object of the present invention is to solve the above technological problems and
control an excessive temperature rise of a pressure roller in a starting step of a
fixing apparatus and thereby prevent a recording material from slipping in the fixing
apparatus so as to stabilize carriage of the recording material and improve quality
of a fixed image.
[0014] In order to attain the above object, a heating apparatus and an image forming apparatus
according to the present invention are characterized by the following configuration.
(1) The image forming apparatus according to the present invention comprises image
forming means for forming an unfixed toner image on the recording material, heating
and fixing means for heating and fixing the above described unfixed toner image on
the recording material, temperature sensing means for sensing the temperature of the
above described heating and fixing means, and power controlling means for controlling
power supplied to the above described heating and fixing means so that the above described
heating and fixing means keeps a fixable temperature at least on fixing operation
based on an output from the above described temperature sensing means, wherein the
above described power controlling means controls power supply to the above described
heating and fixing means based on the above described output from the temperature
sensing element during the time from receipt of a print signal by the image forming
apparatus to performing a heating and fixing process on the recording material so
that, in the case where the temperature of the above described heating and fixing
means rises fast, a temperature control operation for keeping a fixable temperature
should not be protracted before heating and fixing.
(2) Preferably, the above described power controlling means performs a low temperature
control step for controlling the heating and fixing means at a temperature lower than
the fixable temperature or a non-heating step for heating no heating and fixing means
during the time from after receipt of the print signal by the image forming apparatus
to performing the heating and fixing process so as to control power supply to the
heating and fixing means.
(3) Preferably, the temperature of the heating and fixing means is increased more
than once by sandwiching the above described low temperature control step or the above
described non-heating step during the time from after receipt of the print signal
by the image forming apparatus to before performing the heating and fixing process,
and at least by a temperature rise lastly performed thereof, it prepares for the heating
and fixing process of the recording material by rendering the target temperature as
a fixable temperature.
(4) Preferably, the temperature of the heating and fixing means is increased once
after receipt of the print signal by the image forming apparatus so as to determine
performance time of the above described low temperature control step or the above
described non-heating step by this temperature rise behavior.
(5) Preferably, the temperature of the above described heating and fixing means is
increased once to the fixable temperature or a lower temperature than that after receipt
of the print signal by the image forming apparatus.
(6) Preferably, the above described heating and fixing means is comprised of a rotating
heating member capable of rotation and heating the recording material, a rotating
pressure member for forming a nip therewith to heat and pressurize the recording material,
and heat generating means for increasing the temperature of the above described rotating
heating member.
(7) Preferably, the above described rotating heating member is a cylindrical film.
(8) Preferably, the above described rotating heating member is driven by being slaved
to the rotating pressure member.
(9) Preferably, the above described rotating heating member has a conductive member,
and the heating means for heating the above described rotating heating member is magnetic
field generating means including an exciting coil, which has an alternating magnetic
field from the above described magnetic field generating means act upon the above
described conductive member to generate an eddy current so as to cause the above described
rotating heating member to generate heat.
(10) The fixing apparatus according to the present invention for heating and fixing
the unfixed toner image on the recording material introduced from the image forming
means comprises the temperature sensing means for sensing the temperature of the above
described fixing apparatus and the power controlling means for controlling the power
supplied to the above described fixing apparatus so that the above described fixing
apparatus keeps the fixable temperature at least on fixing operation based on the
output from the above described temperature sensing means, wherein the above described
power controlling means controls the power supply to the fixing apparatus based on
the above described output from the temperature sensing element during the time from
after a print start to performing the heating and fixing process on the recording
material so that, in the case where the temperature of the above described fixing
apparatus rises fast, a temperature control operation for keeping a fixable temperature
should not be protracted before the heating and fixing.
(11) Preferably, the above described power controlling means controls the power supply
to the fixing apparatus by performing the low temperature control step for controlling
the temperature of the fixing apparatus at a temperature lower than the fixable temperature
or the non-heating step for heating no heating and fixing means during the time from
after receipt of the print signal by the image forming apparatus to performing the
heating and fixing process.
(12) Preferably, the temperature of the fixing apparatus is increased more than once
by sandwiching the above described low temperature control step or the above described
non-heating step during the time from after the receipt of the print signal by the
image forming apparatus to before performing the heating and fixing process, and at
least by the temperature rise lastly performed thereof, it prepares for the heating
and fixing process of the recording material by rendering the target temperature as
a fixable temperature.
(13) Preferably, the temperature of the fixing means is increased once after the receipt
of the print signal by the image forming means so as to determine performance time
of the above described low temperature control step or the above described non-heating
step by this temperature rise behavior.
(14) Preferably, the temperature of the above described fixing apparatus is increased
once to the fixable temperature or a lower temperature than that after the receipt
of the print signal by the image forming apparatus.
(15) Preferably, the fixing apparatus is comprised of the rotating heating member
capable of rotation and heating the recording material, the rotating pressure member
for forming the nip therewith to heat and pressurize the recording material, and the
heat generating means for increasing the temperature of the above described rotating
heating member.
(16) Preferably, the above described rotating heating member is the cylindrical film.
(17) Preferably, the above described rotating heating member is driven by being slaved
to the rotating pressure member.
(18) Preferably, the above described rotating heating member has the conductive member,
and the above described heat generating means is the magnetic field generating means
including the exciting coil, which has the alternating magnetic field from the above
described magnetic field generating means act upon the above described conductive
member to generate the eddy current so as to cause the above described rotating heating
member to generate heat.
(19) Preferably, it has a first sequence group for sequentially operating at least
following the receipt of the print signal by the image forming apparatus, and a second
sequence group for determining timing of starting the operation according to a sensed
temperature of the fixing apparatus after a predetermined time from the receipt of
the print signal by the image forming apparatus.
(20) Preferably, the above described first sequence group at least includes control
related to the temperature control of the heating and fixing means.
(21) Preferably, the above described second sequence group at least includes the control
related to rotation of a development roller, the rotation of a photosensitive drum
or application of a charging bias.
(22) Preferably, after the above described second sequence group starts the operation,
the above described first sequence group operates by rendering criteria of the above
described second sequence group as their new criteria.
(23) Preferably, the above described image forming means is a color image forming
apparatus for forming an image by performing charging, exposure and development more
than once.
[0015] According to the present invention, in a temperature starting step of the heating
and fixing means (fixing apparatus) on the start of printing, the above described
power controlling means controls the power supply to the above described heating and
fixing means to control an excessive temperature rise of the pressure member based
on the output from the temperature sensing element so that, in the case where the
temperature of the above described heating and fixing means rises fast, a temperature
control operation for keeping a fixable temperature should not be protracted before
the heating and fixing, and the recording material is thereby prevented from slipping.
[0016] Accordingly, it is possible to stably carry the recording material on the fixing
apparatus. In addition, it is also possible to have energy conservation effects such
as reduction in power consumption and a decreased temperature rise in the machine.
[0017] These and other objects, features and advantages of the present invention will become
more apparent upon consideration of the following description of the preferred embodiments
of the present invention taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018]
FIG. 1 is a configuration schematic view of an image forming apparatus according to
a first embodiment;
FIG. 2 is a sectional model view of a side of a major portion of a fixing apparatus
according to the first embodiment;
FIG. 3 is a front model view of the major portion of the fixing apparatus according
to the first embodiment seen from direction A of FIG. 2;
FIG. 4 is a sectional model view of the major portion of the fixing apparatus according
to the first embodiment along a line IV-IV of FIG. 2;
FIG. 5 is a perspective model view of the major portion of the fixing apparatus according
to the first embodiment along a line V-V of FIG. 2;
FIG. 6 is a diagram showing a relationship between magnetic field generating means
and heat capacity Q;
FIG. 7 is a diagram showing a relationship between the magnetic field generating means
and an excitation circuit;
FIG. 8 is a layer constitution model view of a fixing film;
FIG. 9 is a layer constitution model view of the fixing film (with an adiabatic layer);
FIG. 10 is a graph showing the relationship between heat generating layer depth and
electromagnetic wave intensity;
FIG. 11 is a schematic view showing temperature control in a starting step of the
fixing apparatus according to the first embodiment;
FIG. 12 is a temperature control flowchart according to the first embodiment;
FIG. 13 is a schematic view showing the temperature control in the starting step of
the fixing apparatus according to the second embodiment;
FIG. 14 is a temperature control flowchart according to the second embodiment;
FIG. 15 is a schematic view showing the temperature control in the starting step of
the fixing apparatus according to the third embodiment;
FIG. 16 is a temperature control flowchart according to the third embodiment;
FIG. 17 is a longitudinal section showing a schematic configuration of the image forming
apparatus according to the fourth embodiment;
FIG. 18 is a longitudinal section showing a schematic configuration of a process cartridge
according to the fourth embodiment;
FIG. 19 is a perspective view showing the schematic configuration of the process cartridge
according to the fourth embodiment;
FIG. 20 is a timing chart representing operation of the image forming apparatus according
to the fourth embodiment;
FIG. 21 is a flowchart representing the operation of the image forming apparatus according
to the fourth embodiment;
FIG. 22 is a temperature control flowchart according to the fourth embodiment; and
FIG. 23 is a schematic view showing the temperature control in the starting step of
the fixing apparatus according to a past example.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] Hereafter, embodiments of the present invention will be described.
(First Embodiment)
[0020] The first embodiment of the present invention will be described.
(1) Image forming apparatus
[0021] FIG. 1 is a configuration schematic view of an example of an image forming apparatus.
The image forming apparatus according to this embodiment is a color laser printer.
[0022] Reference numeral 101 denotes a photosensitive drum (image bearing member) made of
an organic photosensitive member or an amorphous silicon photosensitive member, which
is driven to rotate counterclockwise as indicated by an arrow at a predetermined carriage
speed (peripheral velocity). The photosensitive drum 101 undergoes a uniform charging
process of predetermined polarity and electric potential on a charging apparatus 102
such as a charging roller in the course of its rotation.
[0023] Next, a charging-processed surface thereof undergoes a scanning exposure process
of target image information with a laser beam 103 outputted from a laser optical box
(laser scanner) 110. The laser optical box 110 outputs the laser beam 103 modulated
(on/off) according to a time series electric digital pixel signal of the target image
information from an unshown image signal generating apparatus such as an image reading
apparatus, and an electrostatic latent image according to the target image information
scanned and exposed on the photosensitive drum 101 surface is formed. Reference numeral
109 denotes a mirror for deflecting an output laser beam from the laser optical box
110 to an exposure position of the photosensitive drum 101.
[0024] In the case of full color image formation, scanning exposure and latent image formation
are performed as to a first color separation component image in a target full color
image such as a yellow component image, and the latent image thereof is developed
as a yellow toner image by the operation of an yellow developing device 104Y of a
four-color developing apparatus 104. The yellow toner image is transferred to the
surface of an intermediate transfer drum 105 in a primary transfer part T1 which is
a contact portion (or a proximity portion) of the photosensitive drum 101 and the
intermediate transfer drum 105. The surface of the photosensitive drum 101 after transferring
the toner image to the intermediate transfer drum 105 is cleaned by a cleaner 107
by removing a sticking residue such as the toner remaining after transferring.
[0025] The above process cycle of charging, scanning exposure, development, primary transfer
and cleaning is sequentially performed as to a second color separation component image
(such as magenta component image, operation of a magenta developing device 104M),
a third color separation component image (such as cyan component image, operation
of a cyan developing device 104C), and a fourth color separation component image (such
as black component image, operation of a black developing device 104Bk) of the target
full color image, and the four-color toner images of yellow, magenta, cyan and black
toner images are sequentially transferred in superimposition to the surface of the
intermediate transfer drum 105 so as to synthesize and form a color toner image in
compliance with the target full color image.
[0026] The intermediate transfer drum 105 has a resilient layer of intermediate resistance
and a surface layer of high resistance provided on a metallic drum, and is driven
to rotate clockwise as indicated by an arrow at the same peripheral velocity as the
photosensitive drum 101 while contacting or in proximity to the photosensitive drum
101 so that a bias potential is given to the metallic drum of the intermediate transfer
drum 105 to transfer the toner image on the photosensitive drum 101 side to the above
described intermediate transfer drum 105 side by means of a potential difference from
the photosensitive drum 101.
[0027] The color toner image formed on the surface of the above intermediate transfer drum
105 is transferred on the surface of a recording material P fed into a secondary transferring
part T2 from an unshown paper feed part in predetermined timing, the above described
secondary transferring part T2 being a contact nip portion of the above described
intermediate transfer drum 105 and a transferring roller 106. The transferring roller
106 sequentially transfers synthetic color toner images by one operation from the
surface side of the intermediate transfer drum 105 to the recording material P side
by supplying a charge of a polarity inverse to the toner from the back of the recording
material P.
[0028] The recording material P having passed through the secondary transferring part T2
is separated from the surface of the intermediate transfer drum 105 to be introduced
to an image heating apparatus (fixing apparatus) 100, where an unfixed toner image
undergoes a heating and fixing process to become a fixed toner image, and is ejected
to an unshown output tray outside the machine. The fixing apparatus 100 will be described
in detail in the next section (2).
[0029] The intermediate transfer drum 105 after transferring the color toner images to the
recording material P is cleaned by a cleaner 108 by having the sticking residue such
as the toner remaining after transferring and paper powder removed. The cleaner 108
is ordinarily held in a non-contact state by the intermediate transfer drum 105, and
is held in a contact state by the intermediate transfer drum 105 in an implementation
process of secondary transferring of the color toner images from the intermediate
transfer drum 105 to the recording material P.
[0030] In addition, the transferring roller 106 is also ordinarily held in the non-contact
state by the intermediate transfer drum 105, and is held in the contact state by the
intermediate transfer drum 105 via the recording material P in the implementation
process of the secondary transferring of the color toner images from the intermediate
transfer drum 105 to the recording material P.
(2) Fixing apparatus 100
[0031] Next, the fixing apparatus 100 provided to the above-mentioned image forming apparatus
will be described.
[0032] The fixing apparatus 100 according to this embodiment adopts a film heating method
using an electromagnetic induction heating method. FIGS. 2 to 5 are the drawings showing
a configuration of a major portion of the fixing apparatus 100 according to this embodiment,
where FIG. 2 is a sectional model view of the side, FIG. 3 is a front model view seen
from direction A of FIG. 2, FIG. 4 is a sectional model view along a line IV-IV of
FIG. 2, and FIG. 5 is a perspective model view showing the section along a line V-V
of FIG. 2 (fixing film not shown) respectively. Hereafter, the fixing apparatus 100
according to this embodiment will be described by using the drawings.
[0033] In FIG. 2, film guides 16a and 16b have a shape of approximately half-circular gutter
in section, forming an approximate cylinder by mutually facing opening sides. A cylindrical
fixing film 10 is loosely fitted to the rim surface side of the film guides 16a and
16b.
[0034] Magnetic field generating means is comprised of magnetic cores 17a, 17b and 17c,
exciting coils 18 and an excitation circuit 27 (see FIG. 7). The magnetic cores 17a,
17b and 17c are placed like a letter T inside the film guide 16a. The exciting coils
18 are held in a space surrounded by the magnetic cores 17a and 17c and the film guide
16a and in a space surrounded by the magnetic cores 17a and 17b and the film guide
16a.
[0035] The magnetic cores 17a, 17b and 17c are members of high permeability, desirably the
materials used for the core of a transformer such as ferrite and permalloy, and the
ferrite of which loss of magnetism over 100 kHz is little is preferably used.
[0036] As shown in FIG. 5, the exciting coils 18 have feeding parts 18a and 18b, and are
connected to the excitation circuit 27 by the feeding parts 18a and 18b. The excitation
circuit 27 is capable of generating high frequencies of 200 kHz to 500 kHz with a
switching power supply. The exciting coils 18 generate an alternating magnetic flux
with an alternating current (high frequency current) supplied from the excitation
circuit 27.
[0037] The fixing film temperature is controlled by a temperature control system including
a temperature sensor 26 so as to keep a predetermined temperature by having current
supply to the exciting coils 18 controlled. The temperature sensor 26 is a temperature
sensing element such as a thermistor. To be more specific, fixing film sensing temperature
information from the temperature sensor 26 is inputted to a control circuit 200, and
the control circuit 200 controls the power supplied from the excitation circuit 27
to the exciting coils 18 so as to have input temperature information from the temperature
sensor 26 kept at a predetermined fixing temperature.
[0038] The film guides 16a and 16b pressurize a fixing nip part N, support the exciting
coils 18 and the magnetic cores 17 as the magnetic field generating means, support
the fixing film 10, and stabilize carriage of the fixing film 10 when rotating. For
the film guides 16a and 16b, a material capable of insulation not hindering passage
of the magnetic flux and bearing a high load is used. As for such a material, a polyimide
resin, a polyamide resin, a polyamide-imide resin, a polyether-ketone resin, a polyether-sulfon
resin, a polyphenylene-sulfite resin, a liquid crystal polymer and so on can be named
for instance.
[0039] As shown in FIG. 2, on the film guide 16b, a slide member 40 longitudinal in a paper
space vertical direction is placed inside the fixing film 10 on a surface side opposite
a pressure roller 30 of the fixing nip part N. To be more specific, the slide member
40 is placed at a position opposite the above described pressure roller 30 via the
fixing film 10 in the fixing nip part N. The slide member 40 is a member for supporting
the fixing film 10 from its inner circular surface against pressurization of the pressure
roller 30 in the fixing nip part N.
[0040] As for the slide member 40, a member of good sliding ability is desirable in order
to decrease slide resistance. For such a member, fluorine resin, glass, boron nitride,
graphite and so on can be named. It is further desirable that the slide member 40
is a member of high thermal conductivity in addition to the sliding ability. Such
a slide member 40 has an effect of rendering longitudinal temperature distribution
even. For instance, in the case of putting a small-size sheet of paper through, an
amount of heat of a non-paper-through part in the fixing film 10 is transmitted to
the slide member 40, and the amount is transmitted to a small-size paper-through part
by longitudinal thermal transmission of the slide member 40. It is also possible to
thereby obtain an effect of reducing power consumption when putting the small-size
sheet of paper through. For such a slide member 40, a composite material such as a
mirror-polished metal such as aluminum or a metal having fluorine resin particles,
boron nitride particles, graphite particles or the like dispersed can be named. In
addition, a member of two-layer configuration wherein a member of high thermal transmission
is coated with a member of good sliding ability, such as aluminum nitride coated with
glass may also be used. In this embodiment, an alumina substrate coated with glass
is used.
[0041] In the case where the slide member 40 is conductive, it is desirable to place it
outside a magnetic field generated from the exciting coils 18 and the magnetic cores
17a, 17b and 17c which are the magnetic field generating means in order not to be
affected thereby. To be more specific, the slide member 40 should be placed at a position
distant from the magnetic core 17b against the exciting coils 18 so as to be placed
outside a magnetic path made by the exciting coils 18.
[0042] In order to further reduce a slide frictional force of the slide member 40 and the
fixing film 10 in the fixing nip part N, it is also possible to place a lubricant
such as a heat-resistant grease between the slide member 40 and the fixing film 10.
Application of the lubricant allows further reduction in slide resistance and longer
life of the apparatus.
[0043] An internal plane part of the film guide 16b has in contact a rigid stay for pressurization
22 having a horizontally long horseshoe sectional shape. In addition, an insulating
member 19 is provided between the rigid stay for pressurization 22 and each of the
magnetic cores 17 for the purpose of insulating them.
[0044] Moreover, flange members 23a and 23b (see FIG. 3) are fitted to the outside of both
the right and left ends of assembly of the film guides 16a and 16b, and are rotatably
mounted while fixing the above described right and left positions. The flange members
23 receive an end portion of the fixing film 10 when rotating and regulate a longitudinal
approach motion of the film guides 16.
[0045] The pressure roller 30 as the rotating pressure member is comprised of a core bar
30a and a heat-resistant resilient material layer 30b such as silicone rubber, fluorine
rubber or fluorine resin, concentrically and integrally formed and coated around the
above described core bar in a state of a roller. The pressure roller 30 is mounted
by having both end portions of the core bar 30a held by bearings rotatably between
chassis-side sheet metals (not shown) of the fixing apparatus.
[0046] In FIG. 3, pressure springs 25a and 25b are mounted in a pressed state between both
the end portions of the rigid stay for pressurization 22 and spring bracket members
29a and 29b on the apparatus chassis (not shown) side respectively, so that a depressing
force is applied to the rigid stay for pressurization 22. Thus, the downside of the
slide member 40 provided to the film guide 16b and the topside of the pressure roller
30 come into contact due to pressure, sandwiching the fixing film 10 so that the fixing
nip part N of a predetermined width is formed.
[0047] The pressure roller 30 is driven by a driving means M to rotate counterclockwise
as indicated by an arrow a in the drawing. The rotation drive of the pressure roller
30 generates frictional force between the pressure roller 30 and an outer surface
of the fixing film 10 so that a torque acts upon the fixing film 10. And the fixing
film 10 rotates around the rims of the film guides 16a and 16b clockwise as indicated
by the arrow b in the drawing at the peripheral velocity approximately equal to that
of the pressure roller 30 while sliding with its internal circular face kept in intimate
contact with the downside of the slide member 40 in the fixing nip part N. To be more
specific, the fixing film 10 is rotated in synchronization with the pressure roller
30 by surface frictional force exerted with the pressure roller.
[0048] As shown in FIG. 5, on a rim surface of the film guide 16a, a plurality of convex
rib parts 16e are formed longitudinally with predetermined intervals. A contact slide
resistance between the rim surface of the film guide 16a and an internal surface of
the fixing film 10 is thereby reduced so as to decrease a rotation load of the fixing
film 10. Such convex rib parts can be formed and provided likewise to the film guide
16b.
[0049] FIG. 6 schematically represents how the alternating magnetic flux is generated by
the magnetic field generating means.
[0050] A magnetic flux C represents a part of the generated alternating magnetic flux. The
magnetic flux C led by the magnetic cores 17a, 17b and 17c generates the eddy current
in a heat generating layer 10a of the fixing film 10 between the magnetic cores 17a
and 17b and between the magnetic cores 17a and 17c. The eddy current has Joule heat
(eddy current loss) generated in the heat generating layer 10a due to specific resistance
of the heat generating layer 10a.
[0051] An amount of heat Q is determined by a density of the magnetic flux C passing through
the heat generating layer 10a, and shows distribution as in the graph in FIG. 6. In
the graph shown in FIG. 6, the vertical axis indicates the position of a circumferential
direction in the fixing film 10 represented by an angle θ with the center of the magnetic
core 17a as 0, and the horizontal axis indicates the amount of generated heat Q in
the heat generating layer 10a of the fixing film 10. Here, it is defined that a heat
generating area H is the area of which maximum amount of the generated heat is Q,
and amount of generated heat is Q/e or larger (e is a base of natural logarithm).
This is the area capable of obtaining the amount of generated heat necessary for a
fixing process.
[0052] As described above, the exciting coils 18 are fed by the excitation circuit 27 so
that the fixing film 10 performs electromagnetic induction heating and rises to the
predetermined temperature. And in a state of being controlled at the predetermined
temperature, the recording material P having an unfixed toner tn image carried from
the image forming means part formed thereon is introduced between the fixing film
10 and the pressure roller 30 so as to have an image surface opposite the fixing film
surface. And in the process of having the recording material P supported and carried
together with the fixing film 10 in the fixing nip part N, the unfixed toner tn on
the recording material P is heated and fixed. After passing through the fixing nip
part N, the unfixed toner tn is cooled to become a fixed toner tn'.
[0053] As the toner containing a low softening substance is used as the toner tn in this
embodiment, an oil application mechanism for preventing an offset is not provided
to the fixing apparatus 100. In the case of using the toner containing no low softening
substance, the oil application mechanism may be provided. In addition, oil application
and cooling separation may be performed even in the case of using the toner containing
the low softening substance.
[0054] A thermo switch 50 which is the temperature sensing element for interrupting feeding
to the exciting coils 18 on a thermorunaway of the fixing apparatus is placed with
no contact at a position opposite to the heat generating area H (see FIG. 6) on an
outer surface of the fixing film 10. Distance between the thermo switch 50 and the
fixing film 10 is approximately 2 mm. Thus, the fixing film 10 will not have a flaw
due to contact with the thermo switch 50, and so it is possible to prevent deterioration
of the fixed image due to enduring use thereof.
[0055] FIG. 7 is a circuit diagram of a thermorunaway preventing circuit used in this embodiment.
The thermo switch 50 is built into this thermorunaway preventing circuit. The thermo
switch 50 is serially connected to a 24V DC power supply and a relay switch 70. If
the thermo switch 50 is turned off, the feeding to the relay switch 70 is interrupted,
and the relay switch 70 operates to interrupt the feeding to the excitation circuit
27 so as to interrupt the feeding to the exciting coils 18.
[0056] According to this embodiment, on the thermorunaway of the fixing apparatus 100 due
to a failure of the temperature control, the fixing apparatus 100 stops in a state
of having the recording material P caught in the fixing nip part N, and even if the
feeding to the exciting coils 18 is continued and the fixing film 10 keeps on generating
heat, no heat is generated in the fixing nip part N with the recording material P
caught, and so the recording material P will not be directly heated, which is different
from the configuration wherein the heat is generated in the fixing nip part N. In
addition, the thermo switch 50 is placed in the heat generating area H having a large
amount of generated heat, so that the relay switch 70 operates to interrupt the feeding
to the exciting coils 18 at a point in time when the thermo switch 50 senses an abnormal
rise in temperature and becomes open. According to this embodiment, no paper gets
ignited since ignition temperature of the paper is around 400 degrees, and thus heat
generation of the fixing film 10 can be stopped. A thermal fuse may also be used in
addition to the thermo switch.
[0057] Hereafter, each of the members used for the above-mentioned fixing apparatus (heating
apparatus) will be described.
2-A) Exciting coils 18
[0058] The exciting coils 18 constituting the magnetic field generating means use a bundle
of a plurality of thin lines made of copper insulated and coated one by one as a conductor
(electric wire) constituting a coil (line ring), which is wound more than once so
as to form the exciting coils.
[0059] As for the coating member for performing insulating coating, it is desirable to use
a heat-resistant coating in consideration of the heat transmission by the heat generation
of the fixing film 10. For instance, it is preferable to use the coating of amide-imide,
polyimide or the like. It is also feasible to pressurize the exciting coils 18 from
the outside so as to improve density.
[0060] As in FIG. 2, the shape of the exciting coils 18 is formed along a curved surface
of the fixing film 10. In addition, the distance between the heat generating layer
of the fixing film 10 and the exciting coils 18 is set to be approximately 2 mm.
[0061] As for the material of the insulating member 19, the one having good insulation performance
and high heat resistance is desirable. For instance, it is preferable to select phenol
resin, fluorine resin, polyimide resin, polyamide resin, polyamide-imide resin, polyether-ketone
resin, polyether-sulfon resin, polyphenylene-sulfite resin, PFA resin, PTFE resin,
FEP resin, LCP resin and so on.
[0062] The distances between the magnetic cores 17a, 17b, 17c/exciting coils 18 and the
heat generating layer of the fixing film 10 should be as close as possible to render
absorption efficiency of the magnetic flux higher. It is desirable if the distance
is 5 mm or less since the fixing film can absorb the magnetic flux with high efficiency.
It is not desirable for the distance to be larger than the above range since the absorption
efficiency of the magnetic flux is remarkably reduced thereby. In addition, as far
as the distance between the heat generating layer of the fixing film 10 and the exciting
coils 18 is 5 mm or less, it is not necessary for the distance to be fixed.
[0063] Moreover, as for 18a and 18b drawn out of the exciting coils 18 in FIG. 5, the insulating
coating is performed on the outside of the bundled lines. 2-B) Fixing film 10 (rotating
heating member)
[0064] FIG. 8 is a layer constitution model view of the fixing film 10 as the heating member
in this embodiment. The fixing film 10 according to this embodiment has a complex
configuration of the heat generating layer 10a as a base layer comprised of an electromagnetic
induction heating metallic film or the like, a resilient layer 10b laminated on the
outer surface thereof, and a mold release layer 10c laminated on the outer surface
thereof. It is also possible to provide primer layers (not shown) among the layers
for the purpose of adhesion between the heat generating layer 10a and resilient layer
10b and adhesion between the resilient layer 10b and mold release layer 10c. Moreover,
in the approximately cylinder-shaped fixing film 10 in FIG. 8, the heat generating
layer 10a is inside for contacting the slide member 40, and the mold release layer
10c is outside for contacting the pressure roller or the recording material (heating
material).
[0065] As previously mentioned, the alternating magnetic flux acts upon the heat generating
layer 10a to generate the eddy current therein so that the heat generating layer 10a
generates heat. The heat is transmitted to the resilient layer 10b and mold release
layer 10c to heat the entire fixing film so that the recording material P put through
the fixing nip part N is heated and the toner image is heated and fixed.
a. Heat generating layer 10a
[0066] While a magnetic or non-magnetic metal may be used for the heat generating layer
10a, the magnetic metal is preferably used. As for such a magnetic metal, a ferromagnetic
metal such as nickel, iron, ferromagnetic stainless, nickel-cobalt alloy or permalloy
is preferably used. In addition, it is also desirable to use a member wherein manganese
is added to the nickel in order to prevent metal fatigue caused by repeated curvature
stress received on the rotation of the fixing film 10.
[0067] As for thickness of the heat generating layer 10a, it should preferably be thicker
than a skin depth σ(m) represented by the following equation and 200 µm or less. If
the thickness of the heat generating layer 10a is in this range, the heat generating
layer 10a can efficiently absorb an electromagnetic wave so that the heat can be efficiently
generated.
[0068] Here, f is a frequency (Hz) of the excitation circuit, µ is permeability of the heat
generating layer 10a, and p is a specific resistance (Ωm) of the heat generating layer
10a.
[0069] The skin depth σ indicates the depth of the absorption of the electromagnetic wave
used for electromagnetic induction, and the intensity of the electromagnetic wave
at a location deeper than that is 1/e or less. To put it inversely, most of the energy
is absorbed to this depth (see the relationship between the heat generating layer
depth and the electromagnetic wave intensity shown in FIG. 10) .
[0070] The thickness of the heat generating layer 10a should more preferably be 1 to 100
µm. In the case where the thickness of the heat generating layer 10a is thinner than
the above range, it will be less efficient since most of the electromagnetic energy
cannot be absorbed. In addition, in the case where the heat generating layer 10a is
thicker than the above range, rigidity of the heat generating layer 10a becomes too
high, and the curvature becomes deteriorated so that it will not be realistic to use
it as a rotating member.
b. Resilient layer 10b
[0071] For the resilient layer 10b, a material of high heat resistance and high thermal
conductivity such as silicone rubber, fluorine rubber or fluoro-silicone rubber is
preferably used.
[0072] The thickness of the resilient layer 10b should preferably be 10 to 500 µm in order
to assure quality of the fixed image. In the case of printing the color image, and
in particular a photographic image, a solid image is formed over large area on the
recording material P. In this case, unevenness in heating arises if the heated surface
(mold release layer 10c) cannot follow projections and depressions on the recording
material P or those on the unfixed toner tn, and unevenness in gloss arises between
the portions of large and small amounts of transmitted heat. To be more specific,
glossiness is high in the portion of large amount of transmitted heat, and it is low
in the portion of small amount thereof. In the case where the thickness of the resilient
layer 10b is smaller than the above range, the above mold release layer 10c cannot
follow the projections and depressions of the recording material P or the unfixed
toner tn so that image gloss unevenness arises. In addition, in the case where the
resilient layer 10b is excessively larger than the above range, the heat resistance
of the resilient layer is too high such that it is difficult to implement a quick
start. The thickness of the resilient layer 10b should more preferably be 50 to 500
µm.
[0073] If hardness of the resilient layer 10b is too high, it cannot follow the projections
and depressions of the recording material P or the unfixed toner tn so that image
gloss unevenness arises. Thus, the hardness of the resilient layer 10b should be 60
degrees (JIS-A) or less, and more preferably 45 degrees (JIS-A) or less.
[0074] Thermal conductivity λ of the resilient layer 10b should preferably be 2.5 x 10
-1 to 8.4 x 10
-1 W/m·°C. In the case where the thermal conductivity λ is smaller than the above range,
the heat resistance is too large such that the rise in temperature in the surface
layer (mold release layer 10c) of the fixing apparatus 10 becomes slow. In the case
where the thermal conductivity λ is larger than the above range, the hardness of the
resilient layer 10b becomes too high or a compression set is apt to arise. It should
more preferably be 3.3 x 10
-1 to 6.3 × 10
-1 W/m·°C.
c. Mold release layer 10c
[0075] For the mold release layer 10c, a material of good mold releasability and high heat
resistance such as fluorine resin, silicone resin, fluoro-silicone rubber, fluorine
rubber, silicone rubber, PFA, PTFE or FEP should preferably be used.
[0076] The thickness of the mold release layer 10c should preferably be 1 to 100 µm. In
the case where the thickness of the mold release layer 10c is thinner than the above
range, unevenness in painting of a coating film arises so that problems such as occurrence
of a portion of low mold releasability and lack in endurability arise. In addition,
in the case where the mold release layer is thicker than the above range, the thermal
conductivity deteriorates. In particular, in the case of using a resin material for
the mold release layer 10c, the hardness of the mold release layer 10c becomes so
high that the resilient layer 10b is no longer effective.
[0077] As shown in FIG. 9, it is also possible, in the fixing film 10 configuration, to
provide an adiabatic layer 10d on the surface side of the heat generating layer 10a
contacting the slide member 40. For the adiabatic layer 10d, a heat-resistant resin
such as fluorine resin, polyimide resin, polyamide resin, polyamide-imide resin, PEEK
resin, PES resin, PPS resin, PFA resin, PTFE resin or FEP resin should preferably
be used. In addition, the thickness of the adiabatic layer 10d should preferably be
10 to 1000 µm. In the case where the thickness of the adiabatic layer 10d is thinner
than 10 µm, no adiabatic effect is obtained and endurability is also insufficient.
On the other hand, if it exceeds 1000 µm, the distance from the magnetic cores 17a,
17b, 17c/exciting coils 18 to the heat generating layer 10a becomes so large that
the magnetic flux is no longer sufficiently absorbed by the heat generating layer
10a. As the adiabatic layer 10d can insulate ' the heat generated in the heat generating
layer 10a so that the heat will not go inside the fixing film, efficiency of heat
supply to the recording material P is better compared to the case of having no adiabatic
layer 10d. Thus, it is possible to control power consumption.
[0078] In addition, it is possible to alleviate the slide resistance between the slide member
40 and the fixing film 10 by constituting the adiabatic layer 10d with a material
of good slidability.
(3) Starting step
[0079] Hereafter, the temperature control in the temperature control starting step of the
fixing apparatus 100 on the start of printing will be described. The control is implemented
by a control circuit part 200 (FIG. 2).
[0080] The control circuit 200 administers overall sequence of the image forming apparatus.
And the control circuit 200 predicts the time required by the fixing apparatus 100
for the rise in temperature to the target temperature.
[0081] FIG. 11 is a schematic view showing the fixing film temperature, setting of the target
temperature of the temperature control, and timing of the recording material reaching
the fixing apparatus in the starting step of the fixing apparatus according to this
embodiment. FIG. 12 is a flowchart of control sequence performed by the control circuit
200.
[0082] Although the fixing apparatus according to this embodiment keeps the temperature
control off to perform no preheating during standby for printing, preheating may also
be performed.
[0083] After receiving the print signal, the image forming apparatus starts the image forming
operation. In a first temperature rising step, it starts the image forming operation
and also starts power supply to the fixing apparatus at the same time. As for the
timing of starting the first temperature rising step, it may be implemented after
the receipt of the print signal, and is not limited to implementing it at the same
time as the start of the image forming operation. The fixing apparatus starts to increase
the temperature aiming at the target temperature, and in this embodiment, the target
temperature of the first temperature rising step is the fixing temperature T
f to be used when fixing the toner on the recording material. And it measures time
t
wu required to increase the temperature to the fixing temperature T
f from the start of the power supply to the fixing apparatus. Once it reaches the target
temperature, the first temperature rising step is finished.
[0084] Next, it determines whether or not the non-heating step can be implemented and time
for implementation thereof. This embodiment is characterized by predicting temperature
rising time of the fixing apparatus in the second temperature rising step rather than
that in the first temperature rising step.
[0085] According to this embodiment, the time t
wu required to increase the temperature to the fixing temperature T
f in the first temperature rising step is measured by setting the target temperature
in the first temperature rising step at the fixing temperature T
f as in the second temperature rising step. The temperature rising time t
wu reflects elements related to the rise in the temperature of the fixing apparatus
such as a surrounding ambient temperature, input voltage and a state of warming up
of the fixing apparatus. The time required for the second temperature rising step
is the temperature rising time t
wu in the first temperature rising step or less considering that the fixing apparatus
is warmed up in the first temperature rising step. Thus, it is possible to assuredly
increase the temperature to the fixing temperature T
f by securing the time t
wu as the time required for the second temperature rising step.
[0086] Whether or not the non-heating step to be performed after finishing the first temperature
rising step can be implemented and the time for implementation t
off are determined by the equation described hereafter.
[0087] If the time from the start of the first temperature rising step until fixing of the
recording material is tp, the time required for the first temperature rising is t
wu, the time for performing the non-heating step is t
off, the time allotted for the second temperature rising is t
wu, and spare time from starting the fixing temperature control step until entry of
the recording material into the fixing nip is tα, the following relationship holds.
[0088] To implement the non-heating step, the following relationship must be fulfilled from
equation (1).
[0089] To be more specific, it is possible to implement the non-heating step if the temperature
rising time t
wu satisfies the following.
[0090] In the case where the temperature rising time t
wu cannot satisfy equation (3), implementation of the non-heating step does not allow
the second temperature rising step to be in time, and so it moves on to the fixing
temperature control step without implementing the non-heating step.
[0091] On the other hand, in the case of implementing the non-heating step, the time for
the non-heating step t
off is the time calculated by the equation (2).
[0092] In the case where the starting step is repeated many times as with intermittent printing,
the fixing apparatus is warmed up and the temperature rising time t
wu becomes shorter, it is possible to render the time for the non-heating step t
off longer. In addition, in the case where processing speed is slow and the time for
carrying the recording material t
p is long as when fixing an OHP film, it is also possible to render the time for the
non-heating step t
off longer.
[0093] After finishing the first temperature rising step, the non-heating step is implemented.
In this step, the power supply to the fixing apparatus is stopped, and the fixing
apparatus is put in a non-heating state. The time for the non-heating step t
off is the time from the timing of finishing the first temperature rising step until
the timing of starting the second temperature rising step mentioned later. The longer
the time for the non-heating step t
off is, the more the temperature rising of the pressure roller can be controled. In addition,
it is also possible to control the temperature rising inside the image forming apparatus
and to reduce the power consumption.
[0094] After finishing the non-heating step, the second temperature rising step is implemented.
The target temperature in the second temperature rising step is the fixing temperature
T
f. The second temperature rising step has the previously measured temperature rising
time t
wu allotted thereto.
[0095] After finishing the second temperature rising step, the fixing temperature control
step is implemented. In the fixing temperature control step, the spare time tα is
provided as the time from starting the fixing temperature control step until entry
of the recording material into the fixing nip. It is possible, during this time, to
control overshooting of the temperature and control oscillation immediately after
the rise in the temperature and also to fix the recording material after stabilizing
the temperature of the fixing apparatus. Then, it keeps the fixing film at the fixing
temperature T
f and fixes the unfixed toner image on the recording material after carrying the recording
material to the fixing apparatus.
[0096] As it is possible, by the above-mentioned temperature control of the fixing apparatus,
to control excessive temperature rising of the pressure roller in the starting step,
it allows slipping of the recording material to be prevented, and it is also feasible
to stabilize the carriage of the recording material and to render the fixed image
of higher quality. In addition, it is also possible to have energy conservation effects
such as reduction in power consumption and a decreased temperature rise in the machine.
(Second Embodiment)
[0097] Hereafter, the temperature control in the starting step of the fixing apparatus on
the start of the printing according to a second embodiment will be described. The
configurations of the image forming apparatus and the fixing apparatus are the same
as those in the first embodiment.
[0098] FIG. 13 is a schematic view showing the fixing film temperature, setting of the target
temperature of the temperature control and the timing of the recording material reaching
the fixing apparatus in the starting step of the fixing apparatus according to this
embodiment. FIG. 14 is a flowchart of a control sequence performed by the control
circuit 200.
[0099] As the temperature control in the first temperature rising step, the second temperature
rising step and the fixing temperature control step is the same as those in the first
embodiment during standby for printing, description thereof will be omitted.
[0100] This embodiment is characterized by providing the low temperature control step for
controlling the target temperature at a temperature T
low which is lower than the fixing temperature Tf instead of providing the non-heating
step for stopping the power supply to the fixing apparatus as in the first embodiment.
It is the same as the non-heating step in the first embodiment as to whether or not
the low temperature control step can be implemented and the method of calculating
implementation time t
low. Thus, a minimum limit temperature of the fixing apparatus is assured even if the
fixing apparatus is excessively cooled in the low temperature control step. Therefore,
it is possible to securely complete the second temperature rising step within the
predetermined time irrespective of fluctuation of the ambient temperature surrounding
the image forming apparatus. To control the rise in the temperature of the pressure
roller, it is preferable that the target temperature T
low in the low temperature control step is low. In addition, although no preheating is
performed during standby for printing in this embodiment, the target temperature T
low in the low temperature control step may be the target temperature during the preheating
in the case of the image forming apparatus and fixing apparatus for performing the
preheating. It is possible, by the above-mentioned temperature control of the fixing
apparatus, to control the excessive temperature rising of the pressure roller in the
starting step.
(Third Embodiment)
[0101] Hereafter, the temperature control in the starting step of the fixing apparatus on
the start of printing according to a third embodiment will be described. The configurations
of the image forming apparatus and the fixing apparatus are the same as those in the
first embodiment.
[0102] FIG. 15 is a schematic view showing the fixing film temperature, setting of the target
temperature of the temperature control and the timing of the recording material reaching
the fixing apparatus in the starting step of the fixing apparatus according to this
embodiment. FIG. 16 is a flowchart of the control sequence performed by the control
circuit 200.
[0103] This embodiment is characterized by calculating the temperature rising time in the
second temperature rising step by acquiring the temperature rising speed in the first
temperature rising step. The temperature rising speed has the elements related to
the temperature rise of the fixing apparatus such as the surrounding ambient temperature
and input voltage reflected thereon.
[0104] First, after the receipt of the print signal, the first temperature rising step is
implemented as in the first embodiment. In this embodiment, the target temperature
in the first temperature rising step is set at a temperature T
pre lower than the fixing temperature T
f. It is thereby possible to shorten the time for the first temperature rising step
and to further control the temperature rise of the pressure roller.
[0105] After the fixing film temperature reaches T
pre, it measures time t
pre required for the temperature to rise from a temperature T
1 at the start of the first temperature rising step to T
pre and a temperature rising speed ΔT/Δt. And it determines whether or not the non-heating
step can be implemented based on the temperature rising time t
pre and the temperature rising speed ΔT/Δt according to the equation described below.
[0106] In addition to the temperature rising time t
pre, if the time for implementing the non-heating step is t
off, the temperature rising time until the fixing temperature calculated based on the
temperature rising speed ΔT/Δt is t
calc, and the spare time from starting the fixing temperature control step until the entry
of the recording material into the fixing nip is tα, the following relationship holds.
[0107] To implement the non-heating step, the following must be fulfilled from equation
(4).
Considering that the fixing film temperature T
pre when finishing the first temperature rising step is equal to the fixing film temperature
T
2 when starting the second temperature rising step, t
calc in the case of t
off = 0 is represented as follows.
[0108] To be more specific, it is possible to implement the non-heating step if the temperature
rising speed ΔT/Δt and the temperature rising time t
pre satisfy the following from equations (5) and (6).
[0109] In the case where the temperature rising speed ΔT/Δt and the temperature rising time
t
pre cannot satisfy equation (7), the non-heating step is not implemented since there
is no sufficient time before the entry of the recording material into the fixing nip.
In this case, the target temperature is immediately switched from T
pre to the fixing temperature Tf to continue the rise in the temperature, and the fixing
temperature control step is performed when it reaches the fixing temperature Tf.
[0110] In the case where the temperature rising speed ΔT/Δt and the temperature rising time
t
pre satisfy equation (7), the non-heating step is implemented after finishing the first
temperature rising step. The time for the non-heating step t
off is the time from the timing of finishing the first temperature rising step until
the timing of starting the second temperature rising step mentioned later, and the
length thereof is determined by the timing of starting the second temperature rising
step. The timing of starting the second temperature rising step according to this
embodiment is determined based on the temperature rising time t
pre and the temperature rising speed ΔT/Δt in the first temperature rising step and the
fixing film temperature T in the non-heating step.
[0111] The following relationship holds from equation (6) immediately before the non-heating
step.
[0112] The following relationship holds immediately after starting the non-heating step
considering that t
off as a parameter to increase from 0 along with elapse of time for the non-heating step
is added.
However, t
off is 0 at this point in time.
[0113] Next, the change of t
off and t
calc during the implementation of the non-heating step is considered. As t
off on the left side of equation (9) is the time for the non-heating step, it increases
from 0 along with the elapse of time. In addition, if the fixing film temperature
when finishing the non-heating step is T, t
calc on the left side of equation (9) is calculated as follows.
As the fixing film temperature T becomes lower than T
pre along with the elapse of the time for the non-heating step, t
calc increases from equation (10).
[0114] To be more specific, as the non-heating step proceeds, the left side of equation
(9) comprised of the sum of the two terms of t
off and t
calc increases.
[0115] Thus, as for the timing of finishing the non-heating step, that is, the timing of
starting the second temperature rising step, the change of the time for the non-heating
step t
off and the fixing film temperature T should be monitored, and it should be the timing
wherein the two terms of t
off and t
calc satisfy the following equation for the first time.
If the fixing film temperature at this time is T
2, t
calc may be represented as follows.
[0116] After finishing the non-heating step, the second temperature rising step is implemented.
The target temperature in the second temperature rising step is the fixing temperature
Tf. The temperature rising time t
calc calculated according to equation (12) is allotted to the second temperature rising
step.
[0117] After finishing the second temperature rising step, the fixing temperature control
step is implemented. In the fixing temperature control step, the spare time tα is
provided from starting the fixing temperature control step until the entry of the
recording material into the fixing nip. This time is utilized to have overshooting
of the fixing film temperature after the rise in the temperature and so on converge
so that the fixing film temperature is stabilized. And the fixing film is kept at
the fixing temperature Tf, and after carrying the recording material to the fixing
apparatus, the unfixed toner image on the recording material is fixed.
[0118] The above-mentioned temperature control of the fixing apparatus can control the excessive
rise in the temperature of the pressure roller in the starting step. In addition,
it is also possible to have the energy conservation effects such as the reduction
in power consumption and the decreased temperature rise in the machine.
(Fourth Embodiment)
[0119] Hereafter, an embodiment of the present invention will be described along the drawings.
(Overall configuration)
[0120] First, the overall configuration of the image forming apparatus will be described
by referring to FIG. 17.
[0121] FIG. 17 is a longitudinal section showing the overall configuration of a laser beam
printer A as an embodiment of the image forming apparatus. The photosensitive drum
101 is driven by an unshown driving means to rotate in the direction of the arrow
in the drawing. Surrounding the photosensitive drum 101, there are the devices placed
such as the charging apparatus 102 for evenly charging the surface of the photosensitive
drum 101 according to the direction of the rotation thereof, a scanner unit 110 for
irradiating a laser beam based on image information to form the electrostatic latent
image on the photosensitive drum 101, the developing apparatus 104 for sticking the
toner on the electrostatic latent image and developing it as the toner image, the
transferring roller 106 for transferring the toner image on the photosensitive drum
101 to the recording material P, and the cleaner 107 for removing the toner remaining
on the surface of the photosensitive drum 101 after transferring.
[0122] Here, the photosensitive drum 101, charging apparatus 102, developing apparatus 104
and cleaner 107 are integrally rendered as a cartridge to form a process cartridge
207.
[0123] The scanner unit 110 is placed approximately in a horizontal direction of the photosensitive
drum 101, and image light corresponding to an image signal by a laser diode (not shown)
is irradiated on a polygon mirror 209 rotated at high speed by a scanner motor (not
shown). It has a configuration wherein the image light reflected on the polygon mirror
209 selectively exposes the surface of the charged photosensitive drum 101 via an
image formation lens 210 so as to form the electrostatic latent image.
[0124] As for the transferring roller 106 placed opposite the photosensitive drum 101, a
metallic core covered with an elastic member such as EPDM (ethylene-propylene-diene
ternary copolymer), urethane rubber or NBR (nitrile butadiene rubber) adjusted to
volume resistivity of 10
7 to 10
11 Ω·cm or so may be used for instance. The transferring roller 106 has a bias of straight
polarity applied thereto from an unshown power supply, and the toner image of negative
polarity on the photosensitive drum 101 is transferred by an electric field due to
this bias to the recording material P in contact with the photosensitive drum 101.
[0125] A paper feeding part 8 feeds and carries the recording material P to the image forming
part, and has a plurality of sheets of the recording material P stored in a paper
feeding cassette 211. When forming the image, a paper feeding roller 212 (half moon
roller) and a pair of registration rollers 213 are driven to rotate according to the
image forming operation, where one sheet of the recording material P in the paper
feeding cassette 211 is separated and fed, and a tip of the recording material P bumps
into the pair of registration rollers 213 and stops once, forms a loop and then is
fed to the nip formed by the transferring roller 106 and the photosensitive drum 101.
Reference numeral 224 denotes a registration sensor, and the image formation is performed
with reference to the point in time when the recording material passes here.
[0126] The fixing apparatus 100 is a quick-start fixing apparatus of the electromagnetic
induction heating method for fixing the toner image transferred to the recording material
P, comprised of the cylindrical fixing film 10 as a rotating member having the heat
generating layer (conductive magnetic member) and the pressure roller 30 in pressurized
contact therewith for giving heat and pressure to the recording material P. To be
more specific, the recording material P having the toner image on the photosensitive
drum 101 transferred thereto is carried by the cylindrical fixing film 10 and the
pressure roller 30 when passing through the fixing apparatus 100, and is also given
the heat and pressure. Thus, the toner image of a plurality of colors is fixed on
the surface of the recording material P. The fixed recording material P is ejected
face down from an ejection part 216 to the outside of the apparatus proper by a pair
of ejection rollers 215.
[0127] The control circuit 200 as control means controls the entire operation of the image
forming apparatus A including the temperature control of the fixing apparatus, and
has a CPU 217, an RAM (Random Access Memory) 218 and an ROM (Read Only Memory) 219.
The ROM 219 has a program for controlling the image forming apparatus and various
types of data written thereto, and the RAM 218 is used for purposes such as storing
the data taken in for controlling the image forming apparatus.
(Process Cartridge)
[0128] A process cartridge will be described in detail by referring to FIGS. 18 and 19.
FIGS. 18 and 19 show a main section and a perspective view of a process cartridge
207 storing the toner. The process cartridge 207 is divided into the photosensitive
drum 101, a photosensitive drum unit 250 having charging means and cleaning means,
and a developing unit 104 having developing means for developing the electrostatic
latent image on the photosensitive drum 101. The photosensitive drum 101 is constituted,
for instance, by applying an organic photoconductive layer (OPC photosensitive member)
on a rim surface of an aluminum cylinder of 30mm diameter.
[0129] The photosensitive drum unit 250 has the photosensitive drum 101 rotatably mounted
on a cleaning frame body 251 via bearings 231 (231a, 231b). The photosensitive drum
101 has the charging apparatus 102 for uniformly charging the surface thereof and
a cleaning blade 260 for removing the toner remaining thereon placed on the rim thereof,
and furthermore, the remaining toner removed from the surface thereof by the cleaning
blade 260 is sequentially sent by a toner feeding mechanism 252 to a waste toner room
253 provided behind the cleaning frame body. And the driving force of an unshown drive
motor is conveyed to one end of the back shown in the drawing so as to rotate the
photosensitive drum 101 counterclockwise as shown according to the image forming operation.
[0130] The developing unit 104 is comprised of a developing roller 240 for rotating in the
direction of the arrow in contact with the photosensitive drum 101, a toner container
241 accommodating the toner and a developing frame body 245. The developing roller
240 is rotatably supported by the developing frame body 245 via a bearing member,
and has a toner supplying roller 243 for rotating in the arrow Z direction in contact
with the developing roller 240 and a developing blade 244 placed on the rim thereof
respectively. Furthermore, the toner container 241 has a toner carriage mechanism
242 for stirring the accommodated toner and carrying it to the toner supplying roller
243 provided therein.
[0131] And the developing unit 104 has a hanging configuration wherein, centering on support
axes 249 provided to bearing members 247, 248 mounted on both ends of the developing
unit 104 respectively, the entire developing unit 104 is reciprocatively supported
against the photosensitive drum unit 250 by a pin 249a, and when in a state of the
process cartridge 207 alone (not mounted on the printer proper), the developing unit
104 is always energized by a pressure spring 254 so as to have the developing roller
240 contact the photosensitive drum 101 with angular moment centering on the support
axes 249. Furthermore, the toner container 241 of the developing unit 104 has a rib
246 for, when creating clearance between the developing roller 240 and the photosensitive
drum 101, being in contact with clearance means (described later) of the printer A
proper integrally provided thereto.
(Fixing Apparatus)
[0132] Description of the fixing apparatus will be omitted since it has the same configuration
as the fixing apparatus 100 used in the first embodiment.
(Drive Configuration)
[0133] Next, an operating mechanism when mounting the process cartridge 207 on the printer
proper A will be described in detail.
[0134] As previously described, the process cartridge 207 always has the developing roller
240 in contact with the photosensitive drum 101 when in a state of the process cartridge
207 alone as in FIG. 18.
[0135] On the other hand, a cam 220 is placed on the deeper side in the inserting direction
of the process cartridge 207 of the printer proper A, for the purpose of creating
clearance between the developing roller 240 and the photosensitive drum 101 against
energization of the developing unit 104. The cam 220 is rotated by an unshown driving
means, and lifts the rib 246 so that the developing roller 240 creates clearance from
the photosensitive drum 101 or releases the lifting of the rib 246 so that the developing
roller 240 contacts the photosensitive drum 101. Normally, if the process cartridge
is mounted on the printer proper, the cam 220 lifts the rib 246 so that the developing
roller 240 creates clearance from the photosensitive drum 101. Accordingly, even in
the case where it is not used for a long time with the process cartridge 207 mounted,
the developing roller 240 always keeps the clearance from the photosensitive drum
101, and so it is possible to securely prevent permanent deformation of a roller layer
caused by keeping the developing roller 240 in contact with the photosensitive drum
101 for a long period of time. The photosensitive drum 101 and the developing roller
240 of the process cartridge 207 mounted on the image forming apparatus proper A can
be separately driven by unshown motors.
(Printing Operation)
[0136] The image forming operation according to this embodiment will be described by using
the schematic view of FIG. 17, the timing chart of FIG. 20 and the flowchart of FIG.
21.
[0137] If the printing operation is started by inputting the print signal to the image forming
apparatus proper (Start, S0), the CPU 217 first starts the temperature control of
the fixing apparatus 100, rotation of the photosensitive drum 101 and rotation of
the scanner 110 (Heat-on, S1). The developing roller 240 remains stopped at this time.
Next, it starts application of the charging bias when predetermined time t_ch elapses
after the photosensitive drum 101 started the rotation (Ch-on, S2). It is because
there is a possibility of creating a memory on the photosensitive drum if the rotation
of the photosensitive drum and application of the charging bias are performed at the
same time.
[0138] Next, the CPU 217 determines whether or not the temperature T of the fixing apparatus
100 has reached a predetermined temperature Ts (S3). The predetermined temperature
Ts is the temperature wherein continuing the temperature control as-is is expected
to allow the temperature of the fixing apparatus 100 to reach the fixing temperature
Tf before the recording material P reaches the fixing apparatus 100 even when the
image forming apparatus is under a low temperature environment or when supplied power
supply voltage is a lower limit value. Hereafter, the predetermined temperature Ts
is called an assured risen temperature. As a matter of course, the assured risen temperature
Ts is set to be lower than the fixing temperature Tf.
[0139] If the temperature T of the fixing apparatus 100 reached the assured risen temperature
Ts, it starts the rotation of the developing roller 240 and application of a development
bias when the predetermined time t dev elapses after the start of the application
of the charging bias (Ch-on) (Dev-on, S4). At this time, if the temperature T of the
fixing apparatus has not reached the assured risen temperature Ts, it continues to
monitor the temperature of the fixing apparatus 100, and if Ts has been reached within
t_dev, it waits until reaching t_dev (S5), and then starts the rotation of the developing
roller 240 and application of the development bias.
[0140] If the temperature reaches the assured risen temperature Ts past t_dev, it starts
the rotation of the developing roller 240 and application of the development bias
at the time of reaching Ts. To be more specific, it delays the timing of the rotation
of the developing roller 240 and application of the development bias to be past t_dev
so as to protract the temperature rising time of the fixing apparatus.
[0141] Normally, if there is a sufficient distance of clearance between the photosensitive
drum 101 and the developing roller 240 so that the developing roller 240 keeps the
clearance, there is no possibility of the toner flying from the developing roller
240 to the photosensitive drum 101 even if the surface of the photosensitive drum
101 is not properly charged. However, it starts the rotation of the developing roller
240 and application of the development bias after the time t_dev when the photosensitive
drum 101 is charged and becomes a normal electric potential in order to prevent the
toner from flying even in the case where the distance of clearance becomes shorter
for some reason. Accordingly, even if the temperature T of the fixing apparatus has
already reached the assured risen temperature Ts within t_dev, it does not perform
the rotation of the developing roller 240 and application of the development bias
until t_dev, so that the printing operation of starting the rotation of the developing
roller 240 and application of the development bias at the time of t_dev is the shortest
printing time.
[0142] After t_dev, the developing roller 240 is put in contact with the photosensitive
drum 101 with reference to Dev_on after the predetermined time (D_R-on, S6), and then
the recording material P is picked up (P-pick, S7) so as to form the image (Print,
S8).
[0143] In the case where a temperature rising state of the fixing apparatus is determined
after picking up the recording material, there is a possibility of lowering printing
accuracy when only extension of the temperature rising time of the fixing apparatus
is performed by stopping the image forming operation once based on a determination
that the temperature rising state thereof is insufficient. Therefore, the temperature
rising state must be determined before picking up the recording material. In the case
where it is determined immediately before picking the recording material up, however,
the rotations of the photosensitive drum and the developing roller have already started,
and if the pickup operation is to be held on standby until the fixing apparatus reaches
the predetermined temperature because the temperature rising state thereof is insufficient,
it means that the photosensitive drum and the developing roller keep on rotating during
that time. As the life of the developing device is significantly affected by the number
of rotations of the developing roller, it is desirable to keep that number at a necessary
minimum. On the other hand, a surface potential of the photosensitive drum once charged
does not attenuate unless a transferring bias is applied or exposure is performed,
and so a discharge for charging does not continue to occur if only the charging bias
is applied and it is rotating. Accordingly, there is no fear that the surface of the
photosensitive drum is cut away and its life becomes shorter due to the discharge.
[0144] Thus, it is possible, by controlling the timing of the start of rotation of the developing
roller 240 and application of the development bias according to the temperature rising
state of the fixing apparatus 100 as in this embodiment, to securely increase the
temperature of the fixing apparatus without shortening the life of the developing
device even when the image forming apparatus is under the low temperature environment
or when the supplied power supply voltage is reduced to the lower limit value.
(Temperature Control Operation)
[0145] Hereafter, the temperature control in the starting step of the fixing apparatus on
the start of the printing in the fourth embodiment will be described. FIG. 22 is a
flowchart of the control sequence performed by the control circuit 200.
[0146] After the receipt of the print signal (S10), the image forming apparatus performs
the power supply to the fixing apparatus (S11), and starts the first temperature rising
step. As for the timing of starting the first temperature rising step, it may be implemented
after the receipt of the print signal, and is not limited to implementing it at the
same time as the start of the image forming operation. The fixing apparatus starts
to increase the temperature aiming at the target temperature, and in this embodiment,
the target temperature of the first temperature rising step is the fixing temperature
Tf to be used when fixing the toner on the recording material.
[0147] Next, it is checked whether or not the fixing film temperature T has reached the
assured risen temperature T
s (<fixing temperature Tf) described in the section "Printing Operation" (S12).
[0148] In the case where the fixing film temperature T is lower than the assured risen temperature
T
s, it is checked whether or not temperature rising time t from the start of the power
supply at the fixing film temperature T is shorter than t_ch + t_dev (S20). t_ch +
t_dev is the shortest time from the start of the power supply to the fixing apparatus
to the timing of the rotation of the developing roller and application of the development
bias.
[0149] In the case where the temperature rising time t exceeds t_ch + t_dev, as described
in the section "Printing Operation", the temperature rising time of the fixing apparatus
is extended until the fixing film temperature T reaches the assured risen temperature
T
s by delaying operation timing of development-related sequences such as the rotation
of the developing roller and application of the development bias (S21, 22). To be
more specific, the control exerted here extends the temperature rising time by delaying
the sequences related to the image formation during the time until the fixing apparatus
reaches the assured risen temperature Ts in the case where it is determined that the
temperature rising of the fixing apparatus is slow. The case where the temperature
rising time t exceeds t_ch + t_dev is a situation where the rise in the temperature
of the fixing apparatus cannot be in time for the fixing process of the recording
material unless the operation timing of the development-related sequences is delayed
as described in the section "Printing Operation", and so it is not possible, as a
matter of course, to secure the time for performing the non-heating step as mentioned
in the first embodiment. Thus, according to this embodiment, it does not proceed to
the steps (S13 to 18) of determining the implementation of the non-heating step in
this case, but it increases the fixing temperature Tf as the target temperature as-is
so as to prepare for the fixing process of the recording material (S19).
[0150] In the case where the fixing film temperature T reaches T
s in a state where the temperature rising time t is t_ch + t_dev or lower, it is increased
as-is targeting the fixing temperature Tf (S13). Thereafter, it proceeds to the step
of determining whether or not the non-heating step can be implemented, but the operation
thereafter (S13 to 18) including this step is the same as the starting step described
in the first embodiment and so the description thereof will be omitted. In addition,
the operation thereafter is not limited to the temperature control of the starting
step described in the first embodiment, but it may also be the temperature control
of the second or third embodiment.
[0151] Moreover, it was described that it does not proceed to the steps (S13 to 18) of determining
the implementation of the non-heating step in the case where the temperature rising
time t exceeds t_ch + t_dev. However, even if it proceeds to the steps of determining
the implementation of the non-heating step, the non-heating step will hardly be implemented
because the time t
WU for increasing the temperature to the fixing temperature Tf is longer than usual.
Thus, in the case where the temperature rising time t exceeds t_ch + t_dev, it may
proceed to the steps of determining the implementation of the non-heating step.
[0152] As described above, it is possible, by performing adequate printing operation and
temperature control operation according to the temperature rising speed of the fixing
apparatus, to constantly and stably supply the fixed image of high quality even if
environmental conditions under which the image forming apparatus and the fixing apparatus
are placed change and the temperature rising speed of the fixing apparatus changes.
[0153] Moreover, the image forming apparatus related to the present invention is not limited
to the above-mentioned embodiments, but it is changeable in various ways within the
outline thereof. To be more specific, while the photosensitive drum and the developing
roller of the process cartridge were driven by separate motors in the above embodiments,
it is also possible to use a method of dividing the drive by utilizing a gear and
a clutch from one motor. In addition, another method such as using the cam instead
of the clearance plate may also be used. Moreover, the timing of starting the fixing
apparatus, photosensitive drum and scanner and the timing of contacting the developing
roller and picking up the recording material may be different from the above order.
While the scanner of an image scanning method was used in the above embodiments, it
is of course possible to use an exposure apparatus employing an LED array. In that
case, the starting operation as that of the scanner is not required, and so the timing
of starting is different from that of the scanner. Furthermore, the present invention
is also applicable to a color image forming apparatus having a plurality of photosensitive
drums and development mechanisms.
<Others>
[0154]
1) Although the apparatus of the film heating method using the electromagnetic induction
heating method is adopted as the fixing apparatus in the embodiments, the fixing apparatus
according to the present invention is not limited thereto. It may also be the apparatus
of the film heating method using a ceramic heater as the heat generating means. It
may also be the apparatus of the heat roller method.
2) There is no restriction as to a formation principle/process of the unfixed toner
image against the recording material of the image forming apparatus, and it is arbitrary.
It may be either a transferring method or a direct method.
[0155] While the invention has been described with reference to the structure disclosed
herein, it is not confined to the details set forth and this application is intended
to cover such modifications or changes as may come within the purposes of the improvements
or the scope of the following claims.
[0156] An image forming apparatus has image forming means for forming an unfixed toner image
on a recording material, heating and fixing means for heating and fixing the unfixed
toner image on the recording material, temperature sensing means for sensing the temperature
of the heating and fixing means, and power controlling means for controlling power
supplied to the heating and fixing means so that the heating and fixing means keeps
a fixable temperature at least on fixing operation based on an output from the temperature
sensing means. The power controlling means controls power supply to the heating and
fixing means based on the output from the temperature sensing element during the time
from receipt of a print signal by the image forming apparatus to performing a heating
and fixing process on the recording material so that, in the case where the temperature
of the heating and fixing means rises fast, a temperature control operation for keeping
the fixable temperature should not be protracted before heating and fixing so as to
control excessive rise in the temperature of the pressure member (pressure roller)
and prevent a media slip.